This invention relates to a reciprocating piston internal combustion engine.
The best known form of reciprocating internal combustion engine is the spark ignition petrol engine as used in many automobiles. It has the advantage of being relatively cheap to manufacture but suffers from low thermal efficiency due inter alia to the direct discharge of its hot exhaust gases to atmosphere. Attempts have been made to improve the thermal efficiency of internal combustion engines, for example the compression ignition diesel engine as used on many commercial vehicles, which uses higher compression ratios than those used on petrol engines, and thereby obtains a lower temperature exhaust. A further engine operating on an even higher compression ratio and thereby lowering the exhaust temperature still further, is the Wishart engine. However, these higher compression ratio engines unfortunately suffer from high friction losses, increased heat losses and pumping (pressure) losses.
An approach alternative to using higher compression ratio engines while at the same time improving on the thermal efficiency of the petrol engine, is to reclaim heat from the exhaust to increase the temperature of the charge admitted to the engine. For example, the automotive gas turbine uses a rotating regenerative heat exchanger having a cold face at one axial end and a hot face at its other end. Air is compressed in a compressor and is transferred from the cold to the hot side of part of the rotating heat exchanger, where fuel is continuously injected to cause spontaneous combustion and drive the power turbine/compressor.
Hot exhaust gases are passed from the hot to the cold side of the other part of the rotating heat exchanger which absorbs heat from the exhaust and then imparts this heat to the incoming compressed air. However, such engines particularly when of small size and operating under part load conditions tend to be inefficient and of course are expensive to manufacture. Another example of an attempt to recover exhaust heat is as an ancillary feature of the Wishart engine mentioned previously. In this form the Wishart engine uses a static recuperative heat exchanger having a cold face at one axial end presented to an external compressor and a hot face at the other end presented to a power reciprocating piston and cylinder which contains a spark plug. Highly compressed air from the compressor passes from the cold side to the hot side of the heat exchanger, where a very high octane number fuel (e.g. methane) is intermittently injected into the heated compressed air, and the hot charge passes into the power cylinder via a transfer valve where it is ignited by the spark plug. Heat is transferred from the exhaust gases passing from the hot to the cold side of the heat exchanger. Thus this form of the Wishart engine retains the disadvantages of the losses associated with high compression ratio engines and, for high thermal efficiency requires an expensive separate compressor means.